1. Field of the Invention:
This invention relates to a novel, effective method for measuring the net weight of a load loaded in a vessel of a vehicle, in particular, a dump truck, and an apparatus for carrying the method into practice.
2. Description of the Prior Art:
Large-sized dump trucks are arranged such that they can be run down slopes by actuating efficiently auxiliary brake such as engine brake etc. In such a case, it is important to measure accurately the net weight of the load on the vehicle. The control of the auxiliary brake depends mainly on the weight of the load on the vehicle.
The conventional method of measuring the weight of the load on a vehicle is to place the dump truck on a platform scale and measure the dead weight thereof, and place again the dump truck under loaded condition on the platform scale and measure the total weight thereof, and then find the net weight of the load by deducting the dead weight from the total weight. This method of measurement is disadvantageous in that measuring operation is troublesome and installation of a large-sized platform scale is required, and at dam construction sites with poor footings, it is difficult or impossible, in most cases, to install a large-sized platform scale.
U.S. Pat. No. 3,428,139 discloses an apparatus, which is alternative to the above-mentioned device using a platform scale, and which comprises an ultrasonic pulse frequency generator mounted on the underside of the bed of a truck, and an ultrasonic reflector mounted on the upper surface of an axle on which vehicle wheels are journaled in opposed relationship to said ultrasonic pulse frequency generator, the arrangement being made such that, based on the principle that as the load on the vehicle increases the distance between the ultrasonic pulse frequency generator and the ultrasonic reflector decreases, the reduced distance is measured by the ultrasonic sound wave, and then the valve thus obtained is converted into the weight of the load.
Further, U.S. Pat. No. 3,878,908 discloses means for measuring wheel load or axle load by means of a shear strain sensing transducer.
Still further, according to U.S. Pat. No. 3,889,767, there is disclosed a weighing device for providing an indication of the load applied to each of axles of the vehicle using at least a pair of electrical strain gauges mounted on the axle on which vehicle wheels are journaled.
The measuring devices disclosed in the above-mentioned U.S. patents each employ vehicle axles as their component parts. However, since dump trucks which make access to construction sites are usually required to run on slopes or inclined lands, it is necessary to provide a method and a device for measuring readily and accurately the weight of the load on them even when they are on a slope. All the measuring devices disclosed in the above-mentioned U.S. patents do not meet this requirement.